A Model Study of the Buoyancy-Driven Circulation in the Gulf of Maine

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  • 1 Department of Oceanography, Texas A&M University, College Station, Texas
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Abstract

A quasi-linear prognostic numerical model has been used to study the three-dimensional baroclinic circulation in the Gulf of Maine region, with a focus on the buoyancy-driven circulation in the inner basins and near the coast where the influence of relatively fresh water from rivers and the Scotian shelf is important. The model uses a horizontal grid with 6-km resolution and a terrain-following vertical coordinate with ten levels to represent the bathymetry and stratification. Several model experiments explore the influences of fluxes from the principal rivers, tidal mixing, and shelf water inflow, beginning with a case with no initial horizontal density gradients and ending with cases initialized by temperature and salinity data from cruises in June of 1982 and 1983, augmented by climatological data. With composite initialization, the model develops a circulation containing realistic elements, including an anticlockwise gyre in the interior of the gulf and a prominent southwestward coastal current. For the 1982 case, characterized by relatively low river runoff, outflow from the Penobscot River guides a branch of the eastern Maine coastal current offshore in a thermohaline front 10–20 km east of Penobscot Bay; a similar dislocation is associated with the Kennebec and Androscoggin Rivers farther to the west. For the comparatively wet spring of 1983, the coastal current continues with less interruption from the Bay of Fundy to Cape Cod and consequently contributes less to the development of the interior circulation.

Abstract

A quasi-linear prognostic numerical model has been used to study the three-dimensional baroclinic circulation in the Gulf of Maine region, with a focus on the buoyancy-driven circulation in the inner basins and near the coast where the influence of relatively fresh water from rivers and the Scotian shelf is important. The model uses a horizontal grid with 6-km resolution and a terrain-following vertical coordinate with ten levels to represent the bathymetry and stratification. Several model experiments explore the influences of fluxes from the principal rivers, tidal mixing, and shelf water inflow, beginning with a case with no initial horizontal density gradients and ending with cases initialized by temperature and salinity data from cruises in June of 1982 and 1983, augmented by climatological data. With composite initialization, the model develops a circulation containing realistic elements, including an anticlockwise gyre in the interior of the gulf and a prominent southwestward coastal current. For the 1982 case, characterized by relatively low river runoff, outflow from the Penobscot River guides a branch of the eastern Maine coastal current offshore in a thermohaline front 10–20 km east of Penobscot Bay; a similar dislocation is associated with the Kennebec and Androscoggin Rivers farther to the west. For the comparatively wet spring of 1983, the coastal current continues with less interruption from the Bay of Fundy to Cape Cod and consequently contributes less to the development of the interior circulation.

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